Industrial trucks are provided with a hydraulic unit to lift loads by the use of a load-carrying means. The unit comprises a driving motor, mostly an electric motor, and a pump driven by the motor as well as a valve assembly. In the simplest case, an easy-action lift cylinder is actuated with a check valve being responsible for holding the load whereas the load is lowered by releasing a return path to the tank from the valve assembly, e.g. via the unblockable check valve.
It has become known already to combine the motor, pump, and valve assembly as a unit within a common casing and to place the casing directly onto a hydraulic tank from which the pump draws in a hydraulic medium. Further, it has been known to feed the flow-back medium not straight to the tank, but route it through a so-called reflux filter during the lowering operation.
Further, it has been known to configure a reflux filter such as to introduce an elongate filter casing (a bell), which contains a filtering element, into the hydraulic tank through an opening. A hose extends from the valve assembly of the hydraulic unit to a hose coupling of the filter casing, either through the tank lid which closes the sealing of the opening or even through a lateral coupling which is formed with a casing which, in turn, is fixed to the tank above the opening. However, a reflux filter of this type has some drawbacks. Possible leaks result because of the externally located couplings of the hose between the hydraulic unit and reflux filter. Furthermore, the reflux hose requires to be disconnected to change the filter. At least two sealing rings are necessary to provide a seal between the reflux hose and the tank or filter casing. Moreover, the known reflux filter necessitates a relative large number of individual components.
It is the object of the invention to provide a hydraulic unit for industrial trucks in which the above-mentioned drawbacks are not encountered and which reduces the constructional and handling effort.